Process for producing synthesis gas



H V. REES PROCESS FOR PRODUCING SYNTHESIS GAS ZOrEmOWm( mml.

May l5, 1951 HARRY V. R EE 5 INVENTOR BY HISATTORN Patented May 15, 1951 PROCESS FOR PRODUCING SYNTHESIS GAS Harry V. Rees, Chappaqua, N. Y., assignor to Texaco Development Corporation, New York, N. Y., a corporation of Delaware Application May 25, 1945, Serial N0. 595,710

6 Claims. 1

This invention relates to the manufacture of hydrocarbons, oxygenated hydrocarbons and the like by a process involving conversion of low boiling hydrocarbons into carbon monoxide and hydrogen, which latter are in turn converted into the aforesaid products.

The invention involves reacting a light hydrocarbon such as methane with CO2 and steam, advantageously formed concurrently and in the same reaction Zone by combustion of a portion of the feed hydrocarbon, to thereby produce a synthesis gas containing CO and H2. The resulting synthesis gas is subjected to the action of a synthesis catalyst so as to effect conversion of C0 and H2 into the desired synthetic products. products of the synthesis reaction may include hydrocarbon gas and also substantial amounts of CO2, CO and H2. Therefore, provision is made for separating these gaseous constituents from the synthesis products and recycling them to the process, as Will be described in more detail.

The gaseous products from the synthesis reaction may include, besides the aforesaid gases, other gaseous materials such as nitrogen, and provision is made for discharging such materials from the system.

A particular feature of the invention has to do with the method for preparing the synthesis gas which will now be described.

In accordance `with the invention, the supply of hydrocarbon feed gas is split into first and second streams. The first stream is mixed with oxygen or an oxygen-containing gas in proportions suitable to provide a combustible mixture. This mixture is subjected to surface combustion on the interior surface of a porous tubular reaction zone constructed from a, refractory material capable of withstanding elevated temperatures. The second stream of hydrocarbon gas is caused to ow within the tubular reaction Zone wherein the second stream hydrocarbons are brought into intimate contact with the hot gaseous products of combustion resulting from the aforesaid surface combustion.

Temperature conditions are maintained within the reaction zone such that the second stream hydrocarbons react with CO2 and steam formed from the surf-ace combustion, thereby producing gaseous products of conversion containing CO and H2.

The resulting stream of synthesis gas, after suitable adjustment of temperature, is passed to a synthesis unit wherein CO and H2 are converted into compounds containing one or more carbon atoms per molecule. As previously set The;

forth, CO2, CO and H2 are removed from the products of the synthesis reaction and recycled all or in part to the feed stream passing through the interior of the aforesaid conversion reaction tube. Provision may be made, if desired, for treating the tail gas from the synthesis reaction so as to separately remove CO2 therefrom, the separated CO2 being recycled all or in part to the inlet of the reaction tube, While residual tail gas comprising mainly CO and Hz is recycled all or in part to provide a portion of the gas stream used for effecting surface combustion.

When nitrogen is present in the oxygen feed gas then provision is made for Venting :nitrogen from the system. This may be done by discharging a, portion of the residual tail gas, With or without first removing CO and H2 therefrom. Provision may be made for recycling residual tail gas, or CO and H2 separated therefrom, to the synthesis reaction.

The invention is of particular application as applied to the type of conversion process described in the copending application, Serial No. 586,004, of Harry V. Rees and Clifford 1G. Ludeman, filed March 31, 1945, for Manufacture of Hydrocarbons and the Like, issued as U. S. Patent No. 2,486,879.

The conversion unit for effecting the conversion of normally gaseous hydrocarbons into synthesis gas advantageously comprises a, porous tube or plurality of porous tubes constructed from a refractory material such as carborunduin. The porous tubes are supported within or extend through a chamber. A combustible gas mixture is maintained Within the chamber to provide a gas blanket surrounding the porous tubes. Sufcient pressure is maintained upon the combustible gas mixture so that it permeates the pores of the porous tubes and thus passes to the interior surfaces thereof upon which it undergoes surface combustion, thereby maintaining the interior surfaces of the tubes at ya state of incandescence.

Advantageously, the composition of the gaseous combustible mixture is such that it is substantially entirely consumed by combustion to form CO2 and steam.

A separate stream of hydrocarbon gas is introduced to the inlet of each porous tube, advantageously after suitable preheating, and caused to ilow therein in intimate mixture with the hot products of surface combustion so that the hydro carbons react with the products of combustion to produce the gaseous mixture containing `CO and H2. If desired, steam may be introduced with the separate stream of hydrocarbon gas in order to assist in the reaction.

An advantage of the invention is that it provides a simple and eiective means for converting hydrocarbons into synthesis gas at relatively high temperatures in the range of 3000 to 3600a F. and higher.

A further advantage is that by employing these high temperatures the conversion is effectively carried out without the necessity for employing conversion catalysts. Y

The invention also provides a simple means for effecting transfer of heat units between the exothermic and endothermic reactions involved.

The Vinvention is eiiectively employed in a process wherein an iron type of catalyst is used in the synthesis reaction and which type of catalyst results in the production of synthesis products containing CO2 in substantial amount. In accordance with the present invention, such CO2 is recycled and ultimately converted into valuable products. Advantage is taken of this CO2 recycle so as to avoid the presence of substantial amounts of nitrogen in the system, since this recycling of CO2 reduces the amount of oxygen feed gas required.

It is also contemplated using substantially pure oxygen gas so as to reduce further the amount of nitrogen entering the system. It is contemplated venting tail gas from theV system in suiicient amount so that the nitrogen content of the synthesis gas being .produced will contain not excess of about mol per cent nitrogen.

YIn order to describe the invention in more detail reference will now be made to the gures of the accompanying drawing.

Figure 1 comprises a diagram of flow for the overall process.

Figure 2 illustrates diagrammatically the construction of a conversion unit used for converting normally gaseous hydrocarbons into synthesis gas.

Referring to Figure 1, a stream of natural gas hydrocarbons consisting essentially of methane, for example, is conducted from a source not shown through a'pipe I. This feed hydrocarbon gas may .comprise hydrocarbons having from 1 to 4 carbon atoms per molecule.

This feed gas stream is split into minor and major proportions, the minor stream passing through a branch pipe 2 while the major stream passes through a pipe 3.

These streams may pass through suitable heat exchange apparatus or a furnace (not indicated inthe drawing) fired by the vented tail gas to which reference will be made later so as to adjust the temperature of each stream to the level desired prior to further processing. Y

The major stream from the pipe 3 passes through a reaction conduit 4 shown in dotted lines within a conversion unit 5.

The minor stream diverted through the pipe 2 flows into the chamber 6 surrounding the reaction tube 4. VThe stream of oxygen or gas rich in free oxygen is conducted, with or without preheating, from a source not shown through a pipe 'I and likewise introduced to the chamber 6 to provide with the minor stream hydrocarbons a combustible mixture of gas.

The combustible gas mixture may be maintained within the chamber 6 at substantially combustion temperature; that is, at a temperature in the range of about 800 to 1200 F. It is 'also maintained under a pressure sufficient to force the gas through the pores of the reaction YtureV ranging Vfrom about 300 to 600 F.

' water occurs.

tube 4 so that it undergoes surface combustion on the interior wall surface of the reaction tube 4, thereby maintaining the wall surface at temperatures in the range 3000 to 3600o F. or more.

l'l'he major stream hydrocarbons thus react with CO2 and steam, formed by the surface combustion and also with CO2 recycled from the synthesis reaction, to produce CO and H2.

The eiiluent stream of synthesis gas leaves the outlet end of the reaction tube l and flows through a pipe 3 to a synthesis unit 9. Before entering the synthesis'reaction, the gas flowing through the pipe 8 is advantageously Vsubjected to heat exchange (in apparatus notV shown) so as to reduce it to a temperature effective for the synthesis reaction; for example, to a tempera- In the synthesis, the gas is subjected to contact with a synthesis catalyst whichrmay comprise about 30%V iron, 60% diatomaceous earth or other supporting material, and about 10% promoting substances such as the oxides ofY thorium; or magnesium. lt will be understood, of course, that instead of iron, other hydrogenating metals such as cobalt and nickel may be employed in the catalyst.

As a result of contact with the synthesis catalyst, CO and H2 react to form hydrocarbons or oxygenated hydrocarbons which are mainly normally liquid, although some gaseous compounds such as methane are formed and a substantial proportion of the CO is converted to CO2, particularly when an iron type of synthesis catalyst is employed. The products of reaction also in-l clude some water. Y

The products of the synthesis reaction aref conducted through a pipe I0 to a vseparator Iii wherein gaseous hydrocarbons, CO2, and unreacted CO and H2 are continuously separated. fromV the liquid constituents. The synthesis productsrare cooled before or after introduction to the separator II so as to eiect condensation of normally liquid compounds and steam.

Assuming that the process is operated to produce hydrocarbons, the liquid hydrocarbons and water accumulating in the separator II are drawn off through a pipe I2 to a separator I3 wherein separation between hydrocarbons and The water is discharged from the system through a pipe I4 while the hydrocarbons are discharged through pipe I5. These hydrocarbons comprise normally liquid constituents including naphtha anclhigher boiling hydrocarbons. Y

The gaseous fraction separated in the separator I I is discharged through a pipe I6. Provision is made for discharging all or a portion i of this gaseous fraction through a pipe Il. Howeiect removal of light hydrocarbons such as propane, butane, pentane and heavier from the residual or tail gas. These light hydrocarbons are discharged through a pipe 20. Y y' The residual gas is conducted through a pipe .2i to a stripping unit 22 adapted to effect removal of CO2 from the gas. This unit may be of the absorption type wherein the CO2 is absorbed in a suitable scrubbing liquid.

The C02 solution is drawn off through a pipe 23 to a still 24 wherein CO2 is liberated from the absorption liquid, the latter being returned through a pipe 25 to the stripping unit 22.

The liberated CO2 is conducted through pipes 2B, 21 and 28 to the previously-mentioned pipe 3 leading to the conversion reaction tube 4. If desired, part of this CO2 may be diverted through pipe 29 and pipe 2 to chamber 6.

The stripped tail gas from which CO2 has been removed is conducted through a pipe 30. This gas may be discharged all or in part from the system or instead may be passed in part through pipes 3, 28 and 3, for return to the conversion reaction. Ii desired, this stripped tail gas containing unreacted CO and H2 may be recycled in part through pipe 32 to the synthesis unit 9.

Also, as indicated, provision may be made for recycling directly to the conversion unit a portion of the tail gas from the top of the separator I I. The desired portion of this gas may pass through pipes i8, 28, 29 and 3 for recycling.

The oxygen gas entering the system through pipe 1 may consist of about 99%; oxygen or may contain from about 50 to 100% oxygen.

t is advantageous to adjust the proportions and compositions of the several reactant streams passing to the conversion unit 5 so that the synthesis gas stream flowing through the pipe 8 will consist essentially of CO and Hz in predetermined proportions; for example, in the proportion of about l molecule of CO to l molecule of H2 such as is desired when using the synthesis gas for the production of normally liquid hydrocarbons over an iron catalyst.

Reference will now be made to Figure 2 which represents diagrammatically a view of a section taken along the diameter of a conversion unit consisting of a single reaction conduit extending through an individual combustible gas chamber.

The numeral 5B designates a single porous reaction tube formed from a refractory material such as carborundum.

The numeral 5I designates a cylindrical metal or ceramic chamber through which the tube 5B extends.

The numeral 52 designates the annular space between the interior surface of the chamber 5I and the exterior surface of the tube 50.

The portion of the tube within the chamber 5I is porous, while the ends thereof projecting beyond the closed ends of the chamber 5I are impervious.

As indicated in Figure 1, a stream of methane gas flows through a pipe I to the inlet end of the tube while a stream of methane and oxygen ows through a pipe 2 to the annular space 52.

The products of conversion comprising CO and H2 are discharged from the outlet end of the tube through pipe B.

In commencing the operation, the mixture of combustible gas is first introduced through pipe i. to provide a blanket of gas in the annular space 52 surrounding the porous portion of the reaction tube. This blanket of gas is maintained under sufficient pressure to force it through the pores of the tube at a rate sufficient to prevent flame propagation baci; through the pores into the annular space. The combustible mixture diiusing through the pores to the inner and porous surface of the tube 5u is ignited at the inner surface so that it undergoes surface combustion, thereby maintaining the inner surface of the tube in an incandescent condition. Combustion thus takes place without the appearance of actual ilame.

The combustible gas chamber 5I may be surrounded with a concentric and outer chamber, not shown, thus providing an annular space beamounts to about 156 pounds per hour.

tween the inner surface of the outer chamber and the outer surface of the cylinder 5I. `This annular space is then used as a preheating chamber for any one of the reaction streams.

It will be understood that instead of a single conversion tube '50, the conversion unit may comprise a plurality of such tubes extending through a closed combustible gas chamber. Also if desired, the unit may be arranged so that surface combustion occurs on the exterior surface of the tubes.

The following is an example in which a hydrocarbon gas having the following composition is charged to produce synthesis gas for conversion with an iron type synthesis catalyst:

N2-0.4 mol per cent CO2-0.1 mol per cent Olli-98.3 mol per cent (EHS-12. mol per cent This gas is divided into two streams, namely a minor stream of 23.5 mol per cent and a major stream of about 76.4 mol per cent. The minor stream is passed through the pipe 2 to the conversion unit 5 at the rate of about 49.25 pounds per hour, while the major stream 'is passed through the pipe 3 at the rate of about 149.71 pounds per hour.

The synthesis gas passing through the pipe 8 to the synthesis unit 9 amounts to about 1000 pounds per hour and has the following composition:

Ela- 42.5 mol per cent DTZ-11.3 mol per cent O2-0.1 mol per cent COL-33.3 mol per cent CO2-3.8 mol per cent H2O-9.0 mol per cent The combined light and heavy hydrocarbons discharged through the pipes I5 and 20, respectively, amount to about 122 pounds per hour and are composed of about 48 pounds of gasoline, 31 pounds of gas oil and 43 pounds wax.

The water discharged through the pipe I4 The tail gas flowing through the pipe 2l amounts to about '722 pounds per hour and has the following composition:

liz-29.99 mol per cent N221.65 mol per cent CO--10.84 mol per cent CO2-25.57 mol per cent H2O-6.46 mol per cent Olii-5.0 mol per cent C2H4--0-04 mol per cent @Hs-0.30 mol per cent Calle- 0.04 mol per cent Galia-0.11 mol per cent The recycled CO2 gas owing through the pipe 26 amounts to about 352 pounds per hour and has the following composition:

liz-1.7 mol per cent Nz0.9 mol per cent CO0.7 mol per cent CO2-89.8 mol per cent H2O-45.5 mol per cent CE1-0.4 mol per cent While mention is made of recycling CO2 to the pipe 3, the operation may be such that all of the CO2 is recycled to the pipe 2, or may be split in any proportions between the two. Likewise, the recycled stripped tail gas may be split in any proportions between pipes 28 and 28a to thereby distribute it'as desired between pipes 2 and 3. The invention is not only applicable to the production of normally liquid hydrocarbons but also'to the production of other compounds such asl oxygenated" hydrocarbons, including 'compounds such as methanol, ethanol, formaldehyde and formic acid, acetic acid, acetone, etc.

It is contemplated that the gaseous feed hydrocarbon entering the combustible mixture zone may be mixed therein with oxygen in stoichio- Y metrical proportions so as to effect substantially complete combustion of the hydrocarbons in the mixture into CO2 and H2O. On the `other hand, a deficiency of oxygen may be used so as to result in the formation of some oxygenated compounds such as aldehydes within the reaction c-onduit or reaction zone. In this latter case, the resulting synthesis gas will-contain this oxygenated material which may pass with CO and.v H2 directly to the synthesis reaction zone.

Obviously many modifications and variations of the invention as above set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed' as are indicated in the appended claims.

I claim: l. The lmethod of preparing synthesis gas containing CO and H2 from normally gaseous hydrocarbone involving reaction of a. feed hydrocarbon with CO2 and H2O during flow through aconduit having a porous wall and formed from a refractory material capable of withstanding elevated temperatures, which comprises surrounding the exterior of said porous wall with a combustible mixture comprising a gaseous hydrocarbon together with free oxygen in relative combining proportion at which water vapor and carbon dioxide comprise the products `of combustion under a pressure such that said combustible mixture passes through said pores to the interior wall surface, effecting surface combustion of said mixture on said interior wall surface thereby forming hot combustionV gas containing CO2 and H2O, introducing t0 the inlet of said conduit a stream of hydrocarbon flow through a reaction conduit having a porous wall and formed from a refractory material capable of withstanding elevated temperatures, which comprises maintaining a supply of hydrocarbon freed gas containing a normally gaseous hydrocarbon, splitting said hydrocarbon feed into rst and second streams, introducing said first stream in admixture with free oxygen in an amount sufficient to burn said hydrocarbon with the formation of essentially H2O and CO2 to a zone surrounding said reaction conduit underV 'pressure sufficient to force the mixture through the porous wall to the interior wall surface of the conduit, effecting surface combustion of said mixture on said interior wall surface such that said mixture is converted to combustiongas containing essentially CO2 and H2O and the said interior Wall surface is maintained at incandescence, introducing said second stream of gaseous hydrocarbon to the inlet of said conduit in the proportions required for combination with said CO2 and H2O to produce essentially CO and H2, eifecting reaction of said second stream hydrocarbons with said CO2 and H2O in the presence of said incandescent surface during flow through the interior of said conduit to form essentially CO and H2 and discharging from the outlet of said conduit a stream'of effluent gas containing CO and H2 in proportions suitable for said synthesis gas. Y

3. In the preparation of a synthesis gas comprising Vhydrogen and car-bon monoxide, the steps which include passing a combustible mixture of hydrocarbon gas together with free oxygen in a relative combining proportion effective to convert the hydrocarbon into combustion products comprising predominantly carbon dioxide and water vapor, through a porous wall formed of refractory material capable of withstandingr elevated temperatures, effecting surface combustion 'of the gaseous mixture at the outlet surface of said porous wall at an elevated temperature in the range of incandescence, simultaneously passing a second stream of gaseous hydrocarbon across said incandescent surface, effecting endothermic oxidation of said second stream of gaseous hydrocarbons by said surface combustion products in the presence of said incandescent surface to form carbon monoxide and hydrogen, and discharging from the vicinity of said surface the productV gas containing substantial proportions of carbon monoxide and hydrogen.

4. In the preparation of synthesis gas containing CO and H2 from normally gaseous hydrocarbons involving reaction of feed hydrocarbons with CO2 and H02, the method which Vcomprises maintaining within a conversion zone a porous Wall formed from a refractory material capable of withstanding elevated temperatures and adapted to provide a surface for effecting surface combustion` maintaining on one side of said 'wall a body of combustible gas comprising a gaseous hydrocarbon together with sufficient free oxygen to burn the hydrocarbon to H2O and CO2 under a pressure such that said gas passes through the pores to the opposite side of said wall, effecting surface combustion-of said collibustible gas on the surface of said opposite side such that said combustible gas is substantially entirely consumed to form hot combustion gas containing CO2 and H2O, directing gaseous hydrocarbons in the proportions required for combination with said CO2 and H2O to produce essentially CO and H2 onto said opposite side of said wall such that said hydrocarbons commingle with said gaseous productsrof combustion in at least close proximity to said surface combustion, effecting reaction of so-directed hydrocarbons with said CO2 and H2O so as to form essentially CO and H2, and discharging from the conversion zone a stream of eiiiuent gas containing CO and H2 in proportions suitable for said synthesis gas.

5. A method of preparing synthesis gas containing CO and H2 from normally gaseous hydrocarbons involving reaction of feed hydrocarbons with CO2 and H2O during flow through a conduit having a porous wall and formed from a refractory material capable of withstanding elevated temperatures, which comprises surrounding the exterior of said porous wall with a combustible gaseous mixture comprising a gasiform hydrocarbon together with free oxygen in a combining proportion sucient to consume said hydrocarbon with the production of essentially H2O and CO2 under a pressure such that said combustible mixture passes through said pores to the interior wall surface, effecting surface combustion oi said mixture at said interior Wall surface such that said mixture is converted essentially to CO2 and H2O at elevated temperature, introducing to the inlet of said conduit a stream of hydrocarbon gas in the proportions required for combination with said CO2 and H2O to produce essentially CO and H2, effecting reaction of so-introduced hydrocarbons with said products ci said combustion during flow within the interior of said conduit so as to "form essentially CO and H2, and discharginar from the outlet of said conduit a stream of eiiluent gas containing CO and H2 in proportions suitable for said synthesis gas.

6. A method of preparing synthesis gas containing CO and H2 from normally gaseous hydrocarbons involving reaction of feed hydrocarbons with CO2 and H2O during flow through a conduit having a porous wall and formed from a refractory material capable of withstanding elevated temperatures, which comprises surrounding the exterior of said porous Wall with a combustible gaseous mixture consisting essentially of methane and oxygen under pressure suiiicient to cause said mixture to pass through said ports to the interior wall surface, effecting surface combustion of methane and oxygen at said interior wall surface relative combining proportion at which the products of combustion are essentially H2O and CO2 such that the mixture is substantially entirely converted Iby combustion to CO2 and H2O,

19 introducing to the inlet of said conduit a separate stream o1' methane in the proportions required for combination with said CO2 and H2O to produce essentially CO and H2, effecting reaction oi so-introduced methane with said products of said combustion during flow within the interior of said conduit to form essentially CO and H2, and discharging from the outlet of said conduit a stream of effluent gas consisting essentially of CO and Hz.

HARRY V. REES.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,957,743 Wietzel et al May 8, 1934 2,062,358 Frolich Dec. 1, 1936 2,106,137 Reed Jan. 1B, 1938 2,243,869 Keith June 3, 1941 2,274,064 Howard Feb. 24, 1942 2,347,682 Gunness May 2, 1944 2,381,696 Shapleigh Aug. 7, 1945 2,431,632 Brandt Nov. 25, 1947 2,436,282 Bennett Feb. 17, 1948 FOREIGN PATENTS Number Country Date 196,972 Great Britain May 4, 1943 OTHER REFERENCES Bone and Townsend: Flame and Combustion in Gases, Longmans, Green and Co., Ltd., London, 1927, pp. 462-464. 

1. THE METHOD OF PREPARING SYNTHESIS GAS CONTAINING CO AND H2 FROM NORMALLY GASEOUS HYDROCARBONS INVOLVING REACTION OF A FEED HYDROCARBON WITH CO2 AND H2O DURING FLOW THROUGH A CONDUIT HAVING A POROUS WALL AND FORMED FROM A REFRACTORY MATERIAL CAPABLE OF WITHSTANDING ELEVATED TEMPERATURES, WHICH COMPRISES SURROUNDING THE EXTERIOR OF SAID POROUS WALL WITH A COMBUSTIBLE MIXTURE COMPRISING A GASEOUS HYDROCARBON TOGETHER WITH FREE OXYGEN IN RELATIVE COMBINING PROPORTION AT WHICH WATER VAPOR AND CARBON DIOXIDE COMPRISE THE PRODUCTS OF COMBUSTION UNDER A PRESSURE SUCH THAT SAID COMBUSTIBLE MIXTURE PASSES THROUGH SAID PORES TO THE INTERIOR WALL SURFACE, EFFECTING SURFACE COMBUSTION OF SAID MIXTURE ON SAID INTERIOR WALL SURFACE THEREBY FORMING HOT COMBUSTION GAS CONTAINING CO2 AND H2O, INTRODUCING TO THE INLET OF SAID CONDUIT A STREAM OF HYDROCARBON GAS IN THE PROPORTIONS REQUIRED FOR REACTION WITH SAID CO2 AND H2O TO FORM ESSENTIALLY CO AND H2, EFFECTING REACTION OF SO-INTRODUCED HYDROCARBONS WITH SAID CO2 AND H2O DURING FLOW THROUGH THE INTERIOR OF SAID CONDUIT TO FORM ESSENTIALLY CO AND H2, AND DISCHARGING FROM THE OUTLET OF SAID CONDUIT A STREAM OF EFFLUENT GAS CONTAINING CO AND H2 IN PROPORTIONS SUITABLE FOR SAID SYNTHESIS GAS. 